JP7351518B2 - LED drive circuit, LED lighting system, and LED drive method - Google Patents

Description

The present invention relates to an LED driving circuit, an LED lighting system, and an LED driving method, and more particularly to an LED driving circuit, an LED lighting system, and an LED driving method that can perform temperature compensation of an LED element.

In recent years, various lighting devices using LED (light emitting diode) elements as light sources have become popular. Compared to conventional light bulbs such as halogen lamps, LED elements have the advantage of significantly lower heat generation and power consumption. Even in lighting devices that require high-intensity illumination light, such as the lighting devices of 2007, LED elements are increasingly being used as light sources instead of light bulbs such as halogen lamps.

Lighting systems for performances on stages and the like often change the brightness of the illumination light, and the brightness of the LED elements depends on the level of a dimming signal such as a DMX (Digital Multiplex) signal input from the console to the lighting system. (Relative luminous intensity) is expressed by a dimming curve. In order to realize the performance lighting as intended by the console operator, the performance lighting system is required to have accurate reproducibility of the dimming curve.
In general, when the relative luminosity is high, even slight changes in brightness are hardly noticeable to the human eye, but when the relative luminosity is low, even slight changes in brightness are perceived by the human eye. be done. As a result, in production on a stage or the like, the brightness at the start of lighting when a spotlight or the like fades in, and the brightness just before turning off when fading out, have important production effects. For this reason, in a lighting device for a performance, especially in the vicinity of the lighting start point of the dimming curve, including the lighting start point of fade-in (light-out point of fade-out), in other words, in the area where the LED element emits light at the minimum luminous intensity, Accurate reproducibility of the light curve is required.

For this reason, in a lighting device for performance, the brightness of the lighting is strictly initialized with respect to the level of the dimming signal at the lighting start point of the dimming curve. At this time, the darker the brightness of the lighting at the lighting start point when fading in (that is, the brightness of the lighting just before turning off when fading out), the smoother the fade in and fade out can be, so the adjustment of the lighting start point can be performed smoothly. In order to make the brightness corresponding to the level of the optical signal as dark as possible, the DC drive current of the LED at the start of lighting is set to exceed the forward voltage of the LED element and be as close to the forward voltage as possible.

Japanese Patent Application Publication No. 2007-201473

However, the relative luminous intensity (brightness) of an LED element generally has a negative temperature characteristic (negative temperature coefficient), and as the temperature of the LED element decreases, the relative luminous intensity increases; The relative luminosity decreases as the temperature increases. As a result, even in a production lighting device using LED elements, the relative luminous intensity of the LED elements varies depending on the ambient temperature.
For example, if the temperature during performance lighting is lower than the temperature at the initial setting, the relative luminous intensity of the LED element will increase compared to the initial setting, and if the LED drive current is the same, the LED element's The brightness (relative luminosity) becomes brighter. On the other hand, if the temperature during stage lighting is higher than the temperature at the initial setting, the relative luminous intensity of the LED element will be lower than at the initial setting. The brightness becomes darker.

In particular, since the illumination is dark at the start of lighting when fading in (immediately before turning off when fading out), even a slight difference in brightness will be recognized. As a result, if the brightness of the lighting at the start of lighting differs from that at the initial setting due to temperature changes, the performance effect will be greatly affected. Furthermore, if the temperature during the performance lighting is higher than the temperature at the initial setting, such as during summer, the relative luminance will decrease, resulting in the LED element not lighting up even if the DMX signal level is raised to the initial setting level for starting lighting. can also occur.
As a result, due to the temperature characteristics of the LED elements, the lighting that is intended by the console operator can be achieved near the lighting start point of the dimming curve, such as at the start of a fade-in or fade-out. There was a risk that it would be difficult to do so.

Here, in the above-mentioned Patent Document 1, in order to compensate for characteristic fluctuations due to temperature changes of color LEDs that can be used in LCD (liquid crystal display) backlights, an NTC (negative temperature coefficient) thermistor is attached to the LED element. Color LED drive circuits connected in series are described. Therefore, even in a lighting device for performance using LED elements, it may be possible to temperature-compensate the dimming curve by connecting an NTC thermistor in series with the LED element in the LED drive circuit of the lighting device.

However, in facilities such as theaters and halls, the temperature environment differs depending on the facility, and the forward voltage and temperature characteristics of individual LED elements vary, so lighting equipment for performances requires so-called on-site adjustment. Simply connecting a thermostat to the LED element in series before shipping at a factory or the like cannot achieve the reproducibility of a dimming curve that is practical for stage production, especially the high reproducibility of the dimming curve near the lighting start point. was difficult.

Furthermore, when dimming a lighting device using an LED element as a light source, the blinking of the LED element is generally controlled by PWM (Pulse Width Modulation).
However, when high-current, high-brightness LED elements of lighting equipment for performances are made to flicker using PWM control, flickering may occur if the blinking frequency of the LED elements is not fast enough, and furthermore, the current cannot be adjusted with high precision. There was a problem.

The present invention has been made in view of the above circumstances, and it is possible to perform dimming by adjusting the current with high precision, and also temperature-compensates the brightness of the LED element near the lighting starting point. It is an object of the present invention to provide an LED drive circuit, an LED lighting system, and an LED drive method that can achieve high reproducibility of dimming curves in the vicinity.

In order to achieve the above object, the LED drive circuit of the present invention is an LED drive circuit that dims the LED element by adjusting the DC drive current flowing through the LED element to which a constant DC voltage is applied, a control voltage generation unit that generates a control voltage value corresponding to the level of a dimming signal input from the outside; a current control unit that controls the DC drive current according to the control voltage value; and a relative luminous intensity of the LED element. a temperature output section that has the same positive and negative temperature characteristics as the temperature characteristics of the LED element and outputs a temperature voltage value corresponding to the ambient temperature of the LED element; A reference voltage value is determined by adding an initial control voltage value initialized as a control voltage value in the control voltage generating section and an initial temperature voltage value outputted as the temperature voltage value from the temperature output section at the time of initial setting. a first addition unit that generates the initial control voltage value and the current temperature voltage value of the LED element outputted from the temperature output unit as the temperature voltage value when the LED element is next turned on after initial setting; a second addition section that generates an addition voltage value by adding the current temperature voltage value corresponding to the ambient temperature of the second addition section; and a comparison section that compares the reference voltage value and the addition voltage value; The control voltage generation unit generates a corrected control voltage value by correcting the initial control voltage value based on the comparison result by the comparison unit so that the added voltage value approaches the reference voltage value, and The second addition section adds the correction control voltage value and the current temperature voltage value to generate a correction addition voltage value, and the comparison section compares the reference voltage value and the correction addition voltage value. The control voltage generation section generates the correction control voltage value until the correction addition voltage value approaches the reference voltage value, the second addition section generates the correction addition voltage value, and the comparison section generates the correction addition voltage value. The method is characterized in that the comparison between the reference voltage value and the corrected addition voltage value is repeated .

Further, the LED lighting system of the present invention includes an LED lighting device including an LED drive circuit of the present invention and an LED element driven by the LED drive circuit, and an operation unit that inputs the dimming signal to the LED lighting device. It is characterized by having the following.

Further, the LED driving method of the present invention includes generating a control voltage value corresponding to the level of the dimming signal, and controlling the DC drive current flowing through the LED element to which the DC constant voltage is applied in accordance with the control voltage value. An LED driving method for dimming the LED element, the method includes an initial setting step of initially setting the control voltage value corresponding to the level of the dimming signal, and after the initial setting, lighting the LED element. and a temperature compensation step of correcting the control voltage value for the level of the dimming signal according to the current ambient temperature of the LED element, and the initial setting step is performed when the LED element starts lighting. a step of setting an initial control voltage value corresponding to a level of a dimming signal; and a step of setting an initial control voltage value corresponding to a level of a dimming signal, and outputting the initial control voltage value from a temperature output section having a temperature characteristic having the same polarity as a temperature characteristic of the relative luminous intensity of the LED element. , a step of generating a reference voltage value by adding an initial temperature voltage value corresponding to the ambient temperature of the LED element at the time of initial setting, and the temperature compensation step includes: (a) adding the initial temperature voltage value corresponding to the ambient temperature of the LED element at the time of initial setting; (b) adding the reference voltage value and the current temperature voltage value corresponding to the ambient temperature of the LED element output from the temperature output unit to generate an addition voltage value; (b) adding the reference voltage value and the addition; (c) correcting the initial control voltage value to generate a corrected control voltage value so that the added voltage value approaches the reference voltage value; (d) generating the corrected control voltage value; a step of adding the corrected control voltage value and the current temperature voltage value to generate a corrected additional voltage value; (e) comparing the reference voltage value and the corrected additional voltage value; (f) the step of The method is characterized by the step of repeating the steps (c) to (e) until the corrected addition voltage value approaches the reference voltage value .

In the LED drive circuit, LED lighting system, and LED drive method of the present invention, a constant DC voltage is applied to the LED element, and the magnitude of the DC drive current flowing through the LED element is controlled according to the control voltage value. Dimming the LED element. Accordingly, unlike the case where the LED element flickers under direct PWM control, the LED element can be dimmed in a flicker-free manner (that is, without any flicker phenomenon occurring).

Furthermore, in the present invention, a temperature voltage value corresponding to the ambient temperature of the LED element is used, which is output from a temperature output section having a temperature characteristic having the same polarity as the temperature characteristic of the relative luminous intensity of the LED element.
In order to accurately reproduce the dimming curve in the lighting start region, the present invention does not simply offset the temperature characteristics of the LED element directly with a thermistor or the like to compensate for the temperature, but instead uses the initial temperature voltage at the initial setting. The current temperature voltage value and the control voltage value at the start of lighting are added to the reference voltage value obtained by adding the value and the initial control voltage value corresponding to the initial control voltage level at the time the LED element starts lighting. The control voltage value is corrected so that the added voltage value becomes closer to the added voltage value. Ideally, the control voltage value is corrected so that the added voltage value matches the reference voltage value.

As a result, the brightness at the starting point of the LED element can be temperature-compensated and kept constant regardless of variations in the temperature characteristics of the relative luminous intensity of the LED element, and the dimming curve near the starting point can be highly reproducible. It is possible to achieve the following.
For example, after the brightness of the lighting is initially set for the level of the dimming signal at the time of starting lighting, even if the temperature is different from the temperature at the time of initial setting, the brightness will be substantially the same as the initially set brightness at the time of starting lighting. The LED element can be made to emit light with equivalent brightness.
As a result, it is possible to accurately reproduce the dimming curve representing the brightness (relative luminous intensity) of the LED element with respect to the level of the dimming signal inputted to the LED drive circuit from the outside.

According to the present invention, it is possible to perform dimming by adjusting the current with high precision, and also to temperature compensate the brightness of the LED element near the lighting start point, so that the dimming curve near the lighting start point is high. It is possible to provide an LED drive circuit, an LED lighting system, and an LED drive method that can achieve reproducibility.

FIG. 1 is a block diagram of an LED lighting system according to an embodiment of the present invention. FIG. 1 is a circuit diagram of an LED drive circuit according to an embodiment of the present invention. (a) is a schematic diagram illustrating the duty ratio of the PWM signal with respect to the dimming signal level, and (b) is a schematic diagram illustrating correction of the duty ratio of the PWM signal. (a) is a schematic diagram of a dimming curve showing the relationship between the level of the dimming signal and the brightness of the LED element, and (b) is a schematic diagram of the lighting control curve near the lighting start point surrounded by the broken line circle C shown in (a). An enlarged view of the dimming curve is shown. (a) is a graph showing the temperature characteristics of the relative luminous intensity of the LED element, and (b) is a graph showing the temperature characteristics of the resistance value of the NCT thermistor. (a) is a graph showing the temperature characteristics of the relative luminous intensity of the LED element, and (b) is a graph showing the temperature characteristics of the temperature voltage value of the temperature output section.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a block diagram of an LED lighting system according to a first embodiment of the present invention. As shown in the figure, the LED lighting system includes an LED lighting device 2 including an LED drive circuit 1 that drives an LED element, and an operation section (console) 3.

The LED lighting device 2 of this embodiment includes, for example, three types of LED elements (not shown in FIG. 1) that constitute a spotlight and output three primary colors of red, green, and blue, respectively. A red LED element has a peak wavelength within a wavelength range of, for example, 570 to 690 nm, a green LED element has a peak wavelength within a wavelength range of, for example, 460 to 620 nm, and a blue LED element has a peak wavelength within a wavelength range of, for example, 420 to 530 nm. It has a peak wavelength within the wavelength range. Here, the peak wavelength of the LED element refers to the wavelength at which the emission intensity is maximum among the emission spectrum of the LED element.
The three types of LED elements are each driven by separate LED drive circuits 1, but in FIG. 1, only one block among the three LED drive circuits 1 is shown as a representative.

The operation unit 3 is provided with a means for adjusting the level of a dimming signal that controls the brightness of the output light of the LED element. This adjustment means can be comprised of a slide bar, rotary knob, toggle switch, or other mechanism. A dimming signal such as a DMX signal is input as an external signal from the operation unit 3 to each LED drive circuit 1 of the LED lighting device 2 at an adjusted level.

FIG. 2 shows a circuit diagram of the LED drive circuit 1. In addition, in the figure, four LED elements 100 connected in series are schematically shown as the LED elements 100 driven by the LED drive circuit 1, but the number of LED elements 100 is not limited to this.

A constant DC voltage (DC+) is applied to the anode side of the LED element 100. The LED drive circuit 1 dims the LED element by adjusting the DC drive current IF flowing through the LED element 100 to which a DC constant voltage is applied, using a dimming signal.
For this purpose, the LED drive circuit 1 includes a control voltage generation section 10 that generates a control voltage value corresponding to the level of a dimming signal (DMX signal level) input from the outside, and a DC drive current that corresponds to the control voltage value. A current control section 20 is provided.

The control voltage generation section 10 includes a PWM signal output section 11 that outputs a PWM signal whose voltage waveform changes over time in a rectangular shape, and a PWM signal output section 11 that outputs the average voltage of the PWM signal output from the PWM signal output section 11 as a control voltage value. It includes first and second averaging sections 12a and 12b, and an arithmetic section 13 that controls the duty ratio of the PWM signal in accordance with the level of the dimming signal input from the outside.
Here, FIG. 3(a) shows the duty ratio of the PWM signal according to the level of the dimming signal. As shown by the polygonal line I in FIG. 3(a), the duty ratio of the PWM signal increases according to the level of the dimming signal.
In this embodiment, the first and second averaging sections 12a and 12b are configured with low-pass filters, and the calculation section 13 is configured with a computer (CPU) 130.

The current control unit 20 includes an N-channel MOSFET (metal-oxide-semiconductor field-effect transistor) 21 as a transistor connected in series between the LED element 100 and the ground potential, and an operational amplifier 22. .
The MOSFET 21 has a drain terminal D as a first terminal connected directly or indirectly to the cathode side of the LED element 100, and a second terminal connected directly or indirectly to the ground potential via a current control resistor R13. A source terminal S as a control terminal and a gate terminal G as a control terminal are provided, and a DC drive current, which is a drain-source current, flows between the drain terminal D and the source terminal in accordance with the voltage applied to the gate terminal G. Control.

A control voltage value is input to the non-inverting input terminal 221 of the operational amplifier (op-amp) 22, and the voltage of the node N1 between the current control resistor R13 and the LED drive circuit element D3 is input to the inverting input terminal 222. It is inputted via a resistor R14, and its output is applied to the gate terminal G of the MOSFET 21 via a resistor R12. As a result, the potential of the gate terminal G increases or decreases in accordance with the increase or decrease in the control voltage value.

In the LED drive circuit 1 of this embodiment, a constant DC voltage is applied to the LED element 100, and the magnitude of the DC drive current IF flowing through the LED element 100 is controlled according to the control voltage value. Dimming. Accordingly, unlike the case where the LED element 100 is directly controlled by PWM and blinks, dimming can be achieved by adjusting the drive current of the LED element 100 with high precision.

In FIG. 4A, a curve I shows a dimming curve representing the relationship between the level of a dimming signal such as a DMX signal externally input to the LED drive circuit 1 and the brightness of the LED element 100. As shown by curve I, the dimming curve increases geometrically as the level of the dimming signal increases from a lighting start point L0 where the level of the dimming signal reaches a predetermined level.

In stage performances, the brightness at the start of lighting when fading in with spotlights, etc., and the brightness just before turning off when fading out have important production effects. (Fade-out point) Accurate reproducibility of the dimming curve is required near the lighting start point of the dimming curve, including L0, that is, in the region where the LED element emits light at the minimum luminous intensity.
Therefore, in a lighting device for performance, the calculation unit 13 of the control voltage generation unit 10 adjusts and initializes the duty ratio of the PWM signal corresponding to the level of the dimming signal input from the outside. The brightness of the illumination with respect to the level of the dimming signal at the lighting start point of the light curve is strictly initialized.

Here, FIG. 5(a) shows the temperature characteristics of the relative luminous intensity of the LED element. The horizontal axis of the figure shows the ambient temperature (° C.) of the LED element, and the vertical axis shows the relative luminous intensity of the LED element in logarithmic form. Note that in the figure, the relative luminous intensity at 25° C. is set to 1.
As schematically shown by curve I in FIG. 5(a), the relative luminous intensity of an LED element generally exhibits a negative temperature characteristic. Therefore, as the temperature of the LED element decreases, the relative luminous intensity increases (becomes brighter), and on the other hand, as the temperature of the LED element increases, the relative luminous intensity decreases (darker). As a result, even in a performance lighting device using an LED element, the relative luminous intensity (brightness) of the LED element varies depending on the ambient temperature of the LED element, which is substantially equal to the temperature of the LED element.
As a result, the dimming curve may deviate from the initial setting depending on the environmental temperature when the lighting device is used.

Here, FIG. 4(b) schematically shows an enlarged view of the dimming curve near the lighting start point, which is surrounded by the ellipse C shown in FIG. 4(a) and requires particularly high reproducibility in stage direction. show.
For example, if the ambient temperature T1 of the LED element 100 during performance lighting is lower than the ambient temperature T0 at the initial setting (T1<T0), the relative luminous intensity of the LED element 100 increases compared to the initial setting, and the LED drive When the current is the same, the brightness (relative brightness) of the LED element 100 with respect to the dimming signal level is brighter than the initial setting dimming curve shown by curve I, as shown by curve II in FIG. 4(b). Become.
On the other hand, if the ambient temperature T2 of the LED element 100 during stage lighting is higher than the ambient temperature T0 at the time of initial setting (T2>T0), the relative luminous intensity of the LED element 100 decreases than at the time of initial setting, and the LED When the drive current is the same, the brightness of the LED element 100 relative to the level of the dimming signal becomes darker than the initial setting dimming curve shown by curve I, as shown by curve III in FIG. 4(b).

In particular, since the illumination is dark at the start of lighting when fading in (immediately before turning off when fading out), even a slight difference in brightness will be recognized. As a result, if the brightness of the lighting at the start of lighting differs from that at the initial setting due to temperature changes, the performance effect will be greatly affected.
For example, in winter, when the temperature during performance lighting is lower than the initial setting temperature, the relative luminous intensity of the LED increases, so that the relative luminous intensity of the LED element at the start of lighting is lower than that at the initial setting. It becomes bright.
In addition, if the temperature during the lighting is higher than the initial setting temperature, such as during summer, the relative luminous intensity will decrease, and the LED elements may not turn on even if the DMX signal level is raised to the initial setting level to start lighting. It can occur.

In order to achieve high reproducibility of the dimming curve, if the ambient temperature T1 of the LED element 100 during performance lighting is lower than the ambient temperature T0 at the time of initial setting (T1<T0), the LED for the DMX signal level must be By reducing the DC drive current IF of the element and lowering the brightness of the LED element, the dimming curve shown by curve II in FIG. 4(b) is corrected, and the dimming curve at the initial setting shown by curve I is obtained. Ideally, it is desirable that they match.
On the other hand, if the ambient temperature T2 of the LED element 100 during performance lighting is higher than the ambient temperature T0 at the time of initial setting (T2>T0), the DC drive current IF of the LED element relative to the DMX signal level is increased and the LED By increasing the brightness of the element, it is necessary to correct the dimming curve shown by curve III in Figure 4(b) to bring it closer to the dimming curve at the initial setting shown by curve I, and ideally it should match It is desirable that the

Therefore, in this embodiment, in order to accurately reproduce the dimming curve of the lighting start region, instead of simply offsetting the temperature characteristics of the LED element directly with a thermistor or the like to compensate for the temperature, the LED element at the initial setting is A reference voltage value is generated by adding the initial temperature voltage value corresponding to the ambient temperature of 100 and the initial control voltage value corresponding to the initially set level of the dimming signal when the LED element 100 starts lighting. The control voltage value is corrected so that the added voltage value obtained by adding the current temperature voltage value and the control voltage value at the time of lighting start approaches the value. Ideally, the control voltage value is corrected so that the added voltage value matches the reference voltage value.

For this purpose, as shown in FIG. 2, the LED drive circuit 1 of this embodiment has a temperature characteristic with the same sign and negative as the temperature characteristic of the relative luminous intensity of the LED element 100, and a temperature voltage corresponding to the ambient temperature of the LED element 100. A temperature output section 30 that outputs a value is provided, and a control voltage corresponding to the initial temperature voltage value output as a temperature voltage value from the temperature output section 30 at the time of initial setting and the level of the dimming signal at the lighting start point of the LED element 100. The first adding unit 40 generates a reference voltage value by adding the initial control voltage value initialized in the control voltage generating unit 10 as a value, and further includes a storage unit 50 for storing the reference voltage value. ing.
Note that in this embodiment, the temperature of the temperature output section 30 is substantially equal to the ambient temperature of the LED element 100.

Further, the LED drive circuit 1 of the present embodiment uses an initial control voltage value and a current value of the LED element outputted as a temperature voltage value from the temperature output section 30 when lighting the LED element after initial setting. The second adding unit 60 generates an added voltage value by adding the current temperature voltage value corresponding to the ambient temperature of 100, and further includes a second adding unit 60 that generates an added voltage value by adding the current temperature voltage value corresponding to the ambient temperature of 100. A comparison section 70 for comparison is provided.

Then, the control voltage generation unit 10 corrects the control voltage value with respect to the level of the dimming signal, based on the comparison result by the comparison unit 70, so that the added voltage value approaches the reference voltage value.

(Temperature output section)
Here, the temperature output section 30 of the LED drive circuit 1 will be explained.
In FIG. 5(b), the temperature characteristic of the resistance value of the NCT thermistor 31 constituting the temperature output section 30 is schematically shown by a curve II. While the relative luminous intensity of the LED element exhibits a negative temperature characteristic with a nearly constant slope with respect to temperature changes, as shown by curve I in FIG. 5(a), the resistance value of the NCT thermistor 31 is , as shown by curve II in FIG. 5(b), exhibits a negative temperature characteristic that increases exponentially as the temperature decreases.

Therefore, in the LED drive circuit of this embodiment, as shown in FIG. A first resistor R11 and an NCT thermistor 31 are connected in series from the first potential side to a potential (for example, ground potential), and a node N2 between the first resistor R11 and the NCT thermistor 31 is provided. Outputs the divided voltage as a temperature voltage value. As a result, an initial temperature value having a negative temperature characteristic is output as the divided voltage of the node N2.

Furthermore, in the temperature output section 30, the resistance value of the second resistor R21 is such that when the ambient temperature of the LED element 100 changes by a predetermined temperature, the amount of change in the temperature voltage value per predetermined temperature due to the temperature characteristics of the NCT thermistor 31 is It is set to substantially match the amount of change per predetermined temperature in the control voltage value required to keep the relative luminous intensity of the LED element 100 constant.
Specifically, the temperature characteristics of the resistance value of the NCT thermistor 31, which increases exponentially, as shown by curve II in FIG. 5(b), are compared with the temperature characteristics shown by curve III in FIG. In order to obtain a negative temperature characteristic that decreases at a substantially constant rate, a second resistor R21 connected in parallel with the NCT thermistor 31 is provided to compress the curve II upward and downward. Furthermore, in this embodiment, a third resistor R20 is provided between the NCT thermistor 31 and the second potential to further adjust the range of change in temperature voltage value due to temperature change in the resistance value of the NCT thermistor 31.
For example, the difference ΔR1 between the resistance value of the NCT thermistor 31 at 0°C and the resistance value at 25°C is equal to the difference ΔR2 between the resistance value at 25°C and the resistance value at 50°C. By doing so, it is possible to obtain a negative temperature characteristic in which the temperature voltage value also decreases at a substantially constant rate as the temperature rises.

In particular, the slope of the temperature characteristic of the relative luminous intensity of the LED element 100, schematically shown by curve I in FIG. 6(a), is different from the temperature voltage value ( It is desirable that the gradient be substantially the same as the slope of the temperature characteristic of the voltage (divided voltage at node N2).
Although the slope of the temperature characteristic of the relative luminous intensity of the LED element 100 is different for each LED element 100 and there is variation, the temperature characteristic of the temperature voltage value can be set to substantially match the temperature characteristic of the LED element 100. For this reason, the second resistor may be a variable resistor and adjusted on-site to substantially match the temperature characteristics of the LED element 100.

(Initial setting process)
Next, an initial setting process for initially setting the control voltage value corresponding to the level of the dimming signal will be explained.
At the time of initial setting, the initial control voltage value V0 is initially set in the control voltage generating section 10 as the control voltage value corresponding to the level of the dimming signal at the lighting start point of the LED element 100.
Specifically, a DMX signal at the level of the dimming signal at the lighting start point of the LED element 100 is input from the outside to the control voltage generation unit 10 of the LED drive circuit 1 . At this time, in the control voltage generation section 10, the calculation section 13 controls the duty ratio of the PWM signal output from the PWM signal output section 11 according to the level of the dimming signal at the lighting start point of the LED element 100, The first averaging unit 12a outputs the average voltage of the PWM signal whose duty ratio is controlled as an initial control voltage value V0.

At this time, the temperature output unit 30 outputs, as the temperature voltage value, an initial temperature voltage value VT0 corresponding to the ambient temperature T0 of the LED element 100 at the time of initial setting.
Then, in the first adding section 40, these initial temperature voltage value VT0 and initial control voltage value V0 are added to generate a reference voltage value S0 (=V0+VT0).
For example, when the initial control voltage value V0=0.3V and the initial temperature voltage value VT0=1.0V, the reference value S0=V0+VT0=0.3+1.0=1.3V.
As shown in FIG. 2, the first adder 40 is configured using an OP amplifier as a non-inverting adder circuit. For this reason, the resistance values of R7 and R8 in FIG. 2 are made equal, and the resistance values of R9 and R10 are also made equal.
In addition, in FIG. 2, illustration of the positive and negative power supply terminals of the OP amplifiers of the first and second adders 40 and 60 is omitted.

The generated reference voltage value S0 is stored in the storage unit 50. In this embodiment, when the memory import switch 51 is turned on, the reference voltage value S0 is stored in the storage section 50.
Note that the storage unit 50 can be configured with various storage media, and may be built into the LED drive circuit, placed outside the LED drive circuit, or connected via a communication line. It may also be provided on a separate network.

(Temperature compensation process)
Next, a temperature compensation process will be described in which the control voltage value for the level of the dimming signal is corrected according to the current ambient temperature of the LED element 100 when the LED element 100 is turned on next time after initial setting.
In this embodiment, in the temperature compensation step, first, a DMX signal at the level of the dimming signal at the lighting start point of the LED element 100 is input to the control voltage generation section 10 of the LED drive circuit 1 . At this time, in the control voltage generation section 10 , the calculation section 13 controls the duty ratio of the PWM signal output from the PWM signal output section 11 according to the level of the dimming signal at the lighting start point of the LED element 100 . In the temperature compensation step, the second averaging section 12b outputs the average voltage of the PWM signal whose duty ratio is controlled as the initial control voltage value V0.

At this time, the temperature output unit 30 outputs the current temperature voltage value VT1 corresponding to the ambient temperature of the LED element 100 at that time.
Then, in the second adder 60, the initial control voltage value V0 and the current temperature voltage value VT1 are added to generate an added voltage value S1 (=V0+VT1).
As shown in FIG. 2, the second adder 60 is configured as a non-inverting adder circuit including an OP amplifier. For this reason, the resistance values of R2 and R3 in FIG. 2 are made equal, and the resistance values of R5 and R6 are also made equal.

On the other hand, the reference voltage value S0 is read out from the storage section 50 by the calculation section 13 with the control voltage generation section 10 and output.
Then, the comparison section 70 compares the reference voltage value S0 and the added voltage value S1. As shown in FIG. 2, the comparison unit 70 is configured as a comparison circuit including an OP amplifier, and outputs an "H" value when the addition voltage value S1 is larger than the reference voltage value S0, and the addition voltage value S1 is the reference voltage value S0. When the voltage value is smaller than S0, an "L" value is output.
The output of the comparator 70 is input to the control voltage generator 10.

If the temperature T1 during the performance lighting is lower than the temperature T0 during initial setting (T1<T0), the added voltage value S1 becomes larger than the reference voltage value S0, and an "H" value is output.
For example, in the case where the initial control voltage value V0 = 0.3V, the initial temperature voltage value VT0 = 1.0, and the reference value S0 = V0 + VT0 = 1.3V at the time of initial setting, the temperature is lower than at the time of initial setting. Sometimes, the temperature voltage value increases, for example, from the initial temperature voltage value 1.0 to the current temperature voltage value VT1=1.5V, resulting in an additional voltage value S1=V0+VT1=0.3+1.5=1.8V. As a result, the added voltage value S1>the reference value S0, and an "H" value is output.

On the other hand, if the temperature T2 during the performance lighting is higher than the temperature T0 at the time of initial setting (T2>T0), the added voltage value S1 becomes smaller than the reference voltage value S0, and the "L" value is output. .
For example, in the case where the initial control voltage value V0 = 0.3V, the initial temperature voltage value VT0 = 1.0, and the reference value S0 = V0 + VT0 = 1.3V at the time of initial setting, the temperature has increased compared to the time of initial setting. Sometimes, the temperature voltage value decreases, for example, from the initial temperature voltage value 1.0 to the current temperature voltage value VT1=0.7V, resulting in the added voltage value S1=V0+VT1=0.3+0.7=1.0V. As a result, the added voltage value S1<the reference value S0, and the "L" value is output.

In the control voltage generation section 10, the calculation section 13 compares the reference voltage value S0 and the added voltage value S1, and sets the control voltage value for the level of the dimming signal so that the added voltage value S1 approaches the reference voltage value S0. to correct.

For example, when the addition voltage value S1 is smaller than the reference voltage value S0, the calculation unit 13 corrects the initial control voltage value V0 by increasing the duty ratio of the PWM signal at a predetermined rate, and corrects the corrected initial control voltage value V0. The voltage value V0+ is output to the second adding section 60.

The second addition section 60 adds the corrected initial control voltage value V0+ and the current temperature voltage value VT1, and outputs the corrected added voltage value S1+ to the comparison section 70.
The comparison section 70 compares the corrected addition voltage value S1+ and the reference voltage value S0, and feeds back the comparison result to the control voltage generation section 10.
This feedback process is repeated until the feedback value output from the comparator 70 changes from the "L" value to the "H" value.

Then, the duty ratio is determined by the correction factor (relative to the initial setting duty ratio) when the feedback value changes from the "L" value to the "H" value, or when the feedback value changes from the "H" value to the "L" value. The corrected PWM signal is input to the first averaging section 12a, and a temperature-compensated control voltage value is output from the first averaging section 12a to the current control section 20.

On the other hand, when the addition voltage value S1 is larger than the reference voltage value S0, the calculation unit 13 corrects the initial control voltage value V0 by decreasing the duty ratio of the PWM signal at a predetermined rate, and The control voltage value V0- is output to the second adding section 60.

The second adder 60 adds the corrected initial control voltage value V0− and the current temperature voltage value VT1, and outputs the corrected added voltage value S1+ to the comparator 70.
The comparator 70 compares the corrected addition voltage value S1− with the reference voltage value S0, and feeds back the comparison result to the control voltage generator 10.
This feedback process is repeated until the feedback value output from the comparator 70 changes from the "H" value to the "L" value.

Then, the duty ratio is determined by the correction factor (relative to the initial setting duty ratio) when the feedback value changes from the "L" value to the "H" value, or when the feedback value changes from the "H" value to the "L" value. The corrected PWM signal is input to the first averaging section 12a, and a temperature-compensated control voltage value is output from the first averaging section 12a to the current control section 20.

FIG. 3(b) shows one pulse of the PWM signal corresponding to the level of the dimming signal shown in FIG. 3(a). In FIG. 3(b), the pulse with the initially set duty ratio is shown by the solid line I, and the pulse whose duty ratio is corrected by the correction factor when the feedback value changes from the "L" value to the "H" value is shown by the broken line II. The pulse whose duty ratio is corrected by the correction factor when the feedback value changes from the "H" value to the "L" value is shown by a broken line III.
The correction factor when the feedback value changes from the "L" value to the "H" value is expressed as the corrected duty ratio d2 for the initially set duty ratio d1 shown in FIG. 3(b), that is, d2/d1. be done.
On the other hand, when the feedback value changes from the "H" value to the "L" value, the correction factor is the corrected duty ratio d3 for the initially set duty ratio d1 shown in FIG. 3(b), that is, d3/ Represented as d1.
In addition, the correction factor d2/d1 when the feedback value changes from the "L" value to the "H" value, or the correction factor d3/d1 when the feedback value changes from the "H" value to the "L" value. The duty ratio may be corrected only in a part of the dimming curve, for example, a lighting start region where the duty ratio is small, or the entire dimming curve may be corrected using the correction factor.

As a result, in order to achieve high reproducibility of the dimming curve, when the temperature T1 during performance lighting is lower than the temperature T0 at the initial setting (T1<T0), the direct current of the LED element 100 relative to the DMX signal level is By reducing the drive current IF and lowering the brightness of the LED element 100, the dimming curve shown by curve II in FIG. 4(b) is corrected to the dimming curve at the initial setting shown by curve I. They can be brought close and ideally matched.

On the other hand, if the temperature T2 during performance lighting is higher than the temperature T0 at the time of initial setting (T2>T0), the brightness of the LED element 100 is increased by increasing the DC drive current IF of the LED element 100 with respect to the DMX signal level. By increasing , it is possible to correct the dimming curve shown by curve III in FIG. can.

In this embodiment, as described above, in the temperature output unit 30, the resistance value of the second resistor R21 is determined by the temperature voltage value due to the temperature characteristics of the NCT thermistor 31 when the ambient temperature of the LED element 100 changes by a predetermined temperature. The amount of change per predetermined temperature is set to substantially match the amount of change per predetermined temperature in the control voltage value required to keep the relative luminous intensity of the LED element 100 constant. Therefore, by correcting the control voltage value of the control voltage generation unit 10 so that the added voltage value S1 substantially matches the reference value S0, the relative luminous intensity of the LED element 100 is kept substantially constant.

Therefore, regardless of variations in the temperature characteristics of the relative luminous intensity of the LED element 100, the brightness at the lighting start point of the LED element 100 can be kept substantially constant by temperature compensation, and the dimming curve near the lighting start point can be adjusted. It is possible to achieve high reproducibility.

Although the embodiments of the present invention have been described above, the present invention can be modified in various ways.
In the embodiment described above, an example was explained in which three types of LED elements that output each of the three primary colors are driven by the LED drive circuit of the present invention, but in the LED lighting system and LED lighting device of the present invention, all LED elements It is not necessary to drive the elements with the LED drive circuit of the present invention, and for example, only one type of LED element may be configured to be driven with the LED drive circuit of the present invention.

Further, although an example has been described in which the current control unit 20 is provided with an N-channel MOSFET as a transistor connected in series between the LED element 100 and the ground potential, the type of transistor is not limited to this, and for example, It may be a P-channel MOSFET, a junction FET, or a bipolar transistor.

Further, in the above embodiment, an example was explained in which only three types of LED elements that output each of the three primary colors were provided, but in the LED lighting device and LED lighting system of the present invention, four or more types of LED elements are provided. You can. For example, in addition to the three types of LED elements of the three primary colors, an LED element that outputs white light may be provided.

Further, in the embodiment described above, an example was explained in which the control voltage generation section was provided with the first averaging section and the second averaging section, but in the LED drive circuit of the present invention, the first averaging section and the second averaging section are provided. One averaging section that also serves as an averaging section may be provided.

The present invention can be applied to various LED element drive circuits, LED lighting devices, and LED lighting systems, and is particularly suitable for application to production lighting devices and lighting systems used in studios or stages. .

1 LED drive circuit 2 LED lighting device 3 Operation section 10 Control voltage generation section 11 PWM signal output section 12a First averaging section 12b Second averaging section 13 Arithmetic section 20 Current control section 21 MOSFET
22 Amplifier (operational amplifier)
30 Temperature output section 31 NCT thermistor 40 First addition section 50 Storage section 60 Second addition section 70 Comparison section 100 LED element 221 Non-inverting input terminal 222 Inverting input terminal D Drain terminal G Gate terminal S Source terminal

Claims (7)

An LED drive circuit that dims an LED element by adjusting a DC drive current flowing through the LED element to which a constant DC voltage is applied,
a control voltage generation unit that generates a control voltage value corresponding to the level of a dimming signal input from the outside;
a current control unit that controls the DC drive current according to the control voltage value;
a temperature output unit having a temperature characteristic having the same positive and negative polarity as the temperature characteristic of the relative luminous intensity of the LED element, and outputting a temperature voltage value corresponding to the ambient temperature of the LED element;
an initial control voltage value initially set in the control voltage generating section as the control voltage value corresponding to the level of the dimming signal at the lighting start point of the LED element; and an initial control voltage value that is initially set in the control voltage generation section as the temperature voltage value from the temperature output section at the time of initial setting. a first addition unit that generates a reference voltage value by adding the outputted initial temperature voltage value ;
After the initial setting, when the LED element is turned on next time, the initial control voltage value and the current temperature corresponding to the current ambient temperature of the LED element, which is output as the temperature voltage value from the temperature output section. a second adding unit that adds the voltage values to generate an added voltage value ;
a comparison unit that compares the reference voltage value and the addition voltage value,
The control voltage generation unit generates a corrected control voltage value by correcting the initial control voltage value based on the comparison result by the comparison unit so that the added voltage value approaches the reference voltage value,
The second addition unit adds the corrected control voltage value and the current temperature voltage value to generate a corrected addition voltage value,
The comparison unit compares the reference voltage value and the corrected addition voltage value,
The control voltage generation section generates the correction control voltage value until the correction addition voltage value approaches the reference voltage value, the second addition section generates the correction addition voltage value, and the comparison section generates the correction addition voltage value until the correction addition voltage value approaches the reference voltage value. Repeating the comparison between the reference voltage value and the corrected addition voltage value
An LED drive circuit characterized by: The control voltage generation section includes:
a PWM signal output section that outputs a PWM signal whose voltage waveform changes over time in a rectangular shape;
an averaging unit that outputs an average voltage of the PWM signal output from the PWM signal output unit as the control voltage value;
an arithmetic unit that controls the duty ratio of the PWM signal in accordance with the level of the dimming signal;
The LED drive circuit according to claim 1, wherein the arithmetic unit corrects the duty ratio of the PWM signal so that the added voltage value approaches the reference voltage value. The current control unit includes a transistor connected in series between the LED element and a ground potential,
The transistor is
a first terminal connected to the LED element;
a second terminal connected to the ground potential;
comprising a control terminal,
controlling the DC drive current flowing between the first terminal and the second terminal according to the voltage applied to the control terminal;
3. The LED drive circuit according to claim 1, wherein the potential of the control terminal increases or decreases in accordance with an increase or decrease in the control voltage value. The temperature output section includes a first resistor and an NCT thermistor connected in series from the first potential side between a first potential and a second potential lower than the first potential,
4. The LED drive circuit according to claim 1, wherein a divided voltage at a node between the NCT thermistor and the first resistor is output as the temperature voltage value. The temperature output section further includes a second resistor connected in parallel with the NCT thermistor,
The resistance value of the second resistor is such that when the ambient temperature of the LED element changes by a predetermined temperature, the amount of change in the temperature voltage value per the predetermined temperature due to the temperature characteristics of the NCT thermistor is the relative value of the LED element. 5. The LED drive circuit according to claim 4, wherein the LED drive circuit is set to substantially match the amount of change per predetermined temperature in the control voltage value required to keep the luminous intensity constant. An LED lighting device comprising the LED drive circuit according to any one of claims 1 to 5 and the LED element driven by the LED drive circuit;
An LED lighting system characterized in that the LED lighting device includes an operation section for inputting the dimming signal. An LED that dims the LED element by generating a control voltage value corresponding to the level of a dimming signal and controlling a DC drive current flowing through the LED element to which a DC constant voltage is applied according to the control voltage value. A driving method,
an initial setting step of initially setting the control voltage value corresponding to the level of the dimming signal;
After the initial setting, when the LED element is next turned on, the control voltage value for the level of the dimming signal is corrected according to the current ambient temperature of the LED element;
The initial setting step includes:
setting an initial control voltage value corresponding to a level of a dimming signal when the LED element starts lighting;
The initial control voltage value and an initial temperature voltage value corresponding to the ambient temperature of the LED element at the time of initial setting, which is output from a temperature output unit having temperature characteristics with the same positive and negative values as the temperature characteristics of the relative luminous intensity of the LED element. a step of generating a reference voltage value by adding the
has
The temperature compensation step includes:
(a) adding the initial control voltage value and the current temperature voltage value output from the temperature output unit and corresponding to the ambient temperature of the LED element to generate an added voltage value;
(b) comparing the reference voltage value and the added voltage value ;
(c) correcting the initial control voltage value to generate a corrected control voltage value so that the added voltage value approaches the reference voltage value ;
(d) adding the corrected control voltage value and the current temperature voltage value to generate a corrected additional voltage value ;
(e) comparing the reference voltage value and the corrected additional voltage value;
(f) repeating the steps (c) to (e) until the corrected addition voltage value approaches the reference voltage value ;
An LED driving method, comprising:

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